In this work, two types of sewage-sludges, aerobically digested and undigested sewage sludge, were used as precursors in the preparation of chars with magnetic property. The two solids were characterized to establish their textural and chemical properties. Due to different elemental composition, chars from the digested sludge were found to contain zeolite-like minerals such as NaP1 zeolite, which enables its abilities of anion exchange, while chars from undigested sewage sludge exhibited a well-degreed graphite structure. 1-Diazo-2-naphthol-4-sulfonic acid (1,2,4-Acid) was used as a model pollutant to investigate its adsorption on prepared chars. The adsorption kinetics of 1,2,4-Acid onto both chars followed pseudo-second-order kinetics. The simulated Langmuir-Freundlich model illustrated that the equilibrium adsorption amount of 1,2,4-Acid was 102.8 and 105.3 mg/g, respectively, at 303 K. The adsorption amount declined on digested chars, whereas kept stable on the other in the presence of sodium chloride, suggesting the diversity in adsorption behavior. (C) 2013 Elsevier Ltd. All rights reserved.